Vacuum tube with coaxial assembly of electrostatic focusing means and electron gun mount

ABSTRACT

The invention comprises an electron gun having an outer cylindrical tube, inside of which a shorter cylindrical tube is positioned. The inner tube is maintained at a different directcurrent potential than the outer tube. The inner tube is positioned inside the outer tube spaced from the ends of the outer tube. Symmetrical electron lenses are then produced at the ends of the inner tube. The use of the outer tube as a mechanical support for the inner tube makes the construction mechanically strong, yet inexpensive.

United States Patent m1 3,560,780

[72] Inventor Johann B. Beeli 2.219,] 1 1 10/1940 Nicoll 313/82 Sylmar,Calif. 2.533.790 12/1950 Grivet 313/82 [2] A pl. No 732,218 2.7409194/1956 Fleming... 3I3/82X [22] Filed May 27, 1968 3.210.145 l0/1965Fyler 313/82X [45] Patented Feb. 2. 1971 2248.558 7/1941 Schlesinger313/82X [73] Assignee International Telephone and Telegraph 2,721,28710/ l 955 Van Ormer. 3 l 3/82X Corporation 3,2414 1 0 4/1966 Oess313/82X New York, N.Y.

a corporation of Delaware [54] VACUUM TUBE WITH COAXIAL ASSEMBLY OFELECTROSTATIC FOCUSING MEANS AND 82BFC, 251, 257

[56] References Cited UNITED STATES PATENTS 2,185,807 l/l940 Gabor eta1. 313/82 Primary ExaminerRoy Lake Assistant Examiner-V. LafranchiAttorneys-C. Cornell Remsen, Jr., Walter]. Baum, Paul W.

Hemminger, Percy P. Lantzy and A. Donald Stolzy ABSTRACT: The inventioncomprises an electron gun having an outer cylindrical tube, inside ofwhich a shorter cylindrical tube is positioned. The inner tube ismaintained at a different direct-current potential than the outer tube.The inner tube is positioned inside the outer tube spaced from the endsof the outer tube. Symmetrical electron lenses are then produced at theends of the inner tube. The use of the outer tube as a mechanicalsupport for the inner tube :makes the construction mechanically strong,yet inexpensive.

BACKGROUND OF THE INVENTION This invention relates to electron dischargedevices. and more particularly to an inexpensive. high strength electrongun.

In the past it has been the practice to form an electron gun from acathode and three axially aligned conductive cylinders. all of thecylinders having the same inside and outside diameters. The middlecylinder is then maintained at a potential different from the outer twoto form focusing electron lenses at the mutually adjacent ends of thetubes.

Due to the use of this prior art construction. extreme care must betaken to align the tubes. The alignment must also be made with aninsulating material. This makes the gun as sembly relatively weak.

SUMMARY OF THE INVENTION In accordance with the device of the presentinvention, the abovedescribed and other disadvantages of prior art areovercome by providing a fixed conductive tube inside of which a secondtube is fixed concentric to the first tube. Conveniently, the secondtube is mounted in insulator rings which are in turn held against theends of the second tube by metal rings that are spot welded to the firsttube. The second tube is thus smaller in diameter than the first tubeand is spaced and insulated therefrom. The second tube is also centrallylocated inside the first tube, the second tube being shorter than thefirst tube.

In accordance with the foregoing, the spot welding of the rings makes itpossible to assemble and completely fabricate the electron gun of theinvention in a few simple steps. Use of the first tube as the structuralsupporting member for the second tube makes the unit unusally strong.

In accordance with another feature of the invention, a small hole isprovided through the wall of the first tube at a position intermediatethe ends of the second tube so that a lead-in wire may be connected tothe first tube through the hole. This makes it possible to createuniformally symmetrical electron lenses at ends of the second tube.

The above-described and other advantages of the present invention willbe understood from the following description when considered inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWING In the drawing, which is to be regarded asmerely illustrative: The FIG. is a longitudinal sectional view through avacuum tube such as a TV camera tube employing the electron gun of thepresent invention.

DESCRIPTION OF OF THE PREFERRED EMBODIMENT In the drawing a vacuum tubeis indicated at having an evacuated envelope 11. The electron gun of theinvention is indicated at 12 in the right end tube 10.

Gun 12 comprises an outer cylindrical metal tube 13, having a hat-shapedcathode 14 with an electron emissive coating 15 thereon. Cathode 14 isheld against the right end of tube 13 with an insulator ring 16sandwiched in between. Ring 16 has an axial projection 17, which extendsinto the interior of the right end of tube 13.

Electron gun 12 also includes an inner metal cylinder 24, which issupported on insulator rings and 26 between metal gs 27 and 28. Metalrings 27 and 28 are spot welded to tube 13.

A power supply 29 connected to a cathode lead 30, to a lead 31 to outertube, and to a lead 32 to inner tube 24. Lead 32 extends into envelope11 and through a hole 33 in the sidewall of tube 13. Hole 33 ispositioned intermediate the ends of tube 24 so that electron lenses atthe ends of tube 24 are symmetrical about the axis of thegun.

In accordance with the foregoing, it WlII be appreciated that the gun 12may be a stacked construction which is easy to assemble and tofabricate. The jaws of a spot welder may be easily inserted into theinterior and over the exterior of tube 13 to spot weld rings 27 and 28thereto. The electron gun 12 therefore, may be manufactured at low cost.Yet, the gun will have considerable mechanical strength because of theuse of unitary tube 13.

Envelope indentations 20 and 21 hold cathode 14 against tube 13.lndentations l8 and 19 support the central portion of tube 13.lndentations 22 and 23 support tube 13 and hold it firmly againstcathode 14.

It is also an advantage of the invention that the small hole 33 does notreduce the mechanical strength of tube 13 substantially. whereas thisenables lead 32 to project therethrough into contact with tube 24. Thisarrangement makes it possible to produce electron lenses at the ends oftube 24 which are symmetrical about the axis of gun l2.

Notwithstanding the foregoing, it will be appreciated that any mountingmeans for tube 24 and cathode 14 may be employed other than those shownand described. Further, hole 33 may be omitted and any other convenientconnecting structure may be provided, if desired.

Many other changes and modifications will suggest themselves to thoseskilled in the art. The invention, is therefore, not to be limited tothe embodiment selected for this disclosure, the true scope of theinvention being defined only in the appended claims.

Iclaim:

1. A vacuum tube having an evacuated envelope, an electron gun mountedin said evacuated envelope and comprising: a first conductive tube fixedin said envelope, said tube having two open ends; a cathode; first meansto fix said cathode in said envelope in a position to supply electronsto one end of said first tube; a second conductive tube open at bothends; second means to fix said second tube inside said first tubecoaxially therewith and in a position insulated therefrom, and spacedfrom the ends thereof, said second tube being smaller in cross sectionand shorter than said first tube; and third means for maintaining saidtubes at different direct-current potentials, said third means includinga conductor, said first tube having a hole therethrough between the endsof said second tube, said conductor extending through said hole in aposition insulated from said first tube but in contact with said secondtube, said second tube having a length sufficiently great and a locationsuch that a radial projection of the crosssectional area of said hole onthe outer surface of said second tube is completely intercepted by saidsecond tube, the entire cross-sectional area of said hole thereby lyingbetween the ends of said second tube, said tubes being thin, concentriccylinders, said cathode including a hat-shaped, metal base having anelectron emissive coating thereon, said base having a radial flange,said first means including a first insulator ring extending over saidone end of said first tube, said envelope having indentations to holdsaid base fiangetight against said first insulator ring, said envelopehaving indentations to support said first tube and to prevent movementthereof away from said cathode, said second means including second andthird insulator rings to fii snugly inside said first tube, said secondtube ends lying on said second and third insulator rings, said secondand third rings having radial flanges, extending over the ends of saidsecond tube to retain the same therebetween, said second means includinga pair of metal rings on the outside of said second and third insulatorrings respectively, said metal rings being fixed to said first tube in aposition to hold said second and third insulator rings snugly againstthe corresponding ends of said second tube.

1. A vacuum tube having an evacuated envelope, an electron gun mountedin said evacuated envelope and comprising: a first conductive tube fixedin said envelope, said tube having two open ends; a cathode; first meansto fix said cathode in said envelope in a position to supply electronsto one end of said first tube; a second conductive tube open at bothends; second means to fix said second tube inside said first tubecoaxially therewith and in a position insulated therefrom, and spacedfrom the ends thereof, said second tube being smaller in cross sectionand shorter than said first tube; and third means for maintaining saidtubes at different direct-current potentials, said third means includinga conductor, said first tube having a hole therethrough between the endsof said second tube, said conductor extending through said hole in aposition insulated from said first tube but in contact with said secondtube, said second tube having a length sufficiently great and a locationsuch that a radial projection of the cross-sectional area of said holeon the outer surface of said second tube is completely intercepted bysaid second tube, the entire cross-sectional area of said hole therebylying between the ends of said second tube, said tubes being thin,concentric cylinders, said cathode including a hatshaped, metal basehaving an electron emissive coating thereon, said base having a radialflange, said first means including a first insulator ring extending oversaid one end of saiD first tube, said envelope having indentations tohold said base flangetight against said first insulator ring, saidenvelope having indentations to support said first tube and to preventmovement thereof away from said cathode, said second means includingsecond and third insulator rings to fit snugly inside said first tube,said second tube ends lying on said second and third insulator rings,said second and third rings having radial flanges, extending over theends of said second tube to retain the same therebetween, said secondmeans including a pair of metal rings on the outside of said second andthird insulator rings respectively, said metal rings being fixed to saidfirst tube in a position to hold said second and third insulator ringssnugly against the corresponding ends of said second tube.